Improvement Of Microwave Dielectric Properties Research Articles

Anti-reduction mechanism of Ba4.2Sm9.2Ti18O54 ceramics by Mg2+/Ta5+ complex ion co-doping

In this work, a novel anti-reduction mechanism was put up by substituting (Mg1/3Ta2/3)4+ complex ion for Ti4+ ion in Ba4.2Sm9.2Ti18-x(Mg1/3Ta2/3)xO54 (0 ≤ x ≤ 0.1) ceramics. The influence of (Mg1/3Ta2/3)4+ complex ion on the sintering behavior, crystal structure, anti-reduction mechanism and microwave dielectric properties of Ba4.2Sm9.2Ti18-x(Mg1/3Ta2/3)xO54 ceramics was investigated. The results indicated that Ba4.2Sm9.2Ti18-x(Mg1/3Ta2/3)xO54 ceramics maintained a typical single-phase tungsten bronze structure. After doping, the ceramic exhibited dense structure and typical columnar grains. Raman spectroscopy and XPS analysis confirmed the reduction of oxygen vacancies and obtained a 7.86 % decrease of Ti3+ ions. Due to the anti-reduction of Ti4+ ions, Ba4.2Sm9.2Ti18-x(Mg1/3Ta2/3)xO54 ceramics possessed an improvement in microwave dielectric properties. In Ba4.2Sm9.2Ti18-x(Mg1/3Ta2/3)xO54 (0 ≤ x ≤ 0.1) ceramics, the Ba4.2Sm9.2Ti17·95(Mg1/3Ta2/3)0.05O54 (x = 0.05) ceramic sintered at 1350 °C for 4 h showed the best integrated microwave dielectric properties with εr = 79.62, Qf = 10,450 GHz and τf = −10.66 ppm/°C.

Investigation on the improvement of microwave dielectric properties of plasma-prepared fluoropolymer-coated CaTiO3-filled PTFE composites

High-performance polymer matrix composites preparation has been urgently hampered by poor interfacial adhesion between two phases. In this article, a thorough analysis of the microstructure and overall properties of composites made of polytetrafluoroethylene filled with fluorocarbon polymer film-coated CaTiO3 was conducted. The similar fluorocarbon molecular structure of CaTiO3 surface and PTFE provides a bridge between the two, significantly improving and promoting the microstructure and interface adhesion of the composite. The comprehensive properties of modified composites are obviously superior to those of untreated composites. Composites filled with 30 wt% CaTiO3 have an excellent dielectric constant at 5.53, acceptable dielectric loss at 0.0047, an outstanding heat resistance index of 281.1°C, and relatively low hygroscopicity of 0.10%. At the same time, the mechanical properties are maintained at a high application level, which makes them promising for microwave devices.

Improvement of Microwave Dielectric Properties by Impact of Sodium Ion Doping in Complex Oxides for Polymer Composites

The research presented in this study focuses on the dielectric properties of complex oxide-filled epoxy, polyurethane, and silicone rubber composites. Specifically, we investigated various compositions of (1-x) CaWO4-xNa2WO4 (x = 0, 0.2, 0.4), in addition to Na0.5Bi0.5Mo0.5W0.5O4 and Bi2Mo0.5W0.5O6. These complex oxide materials were meticulously synthesized through a solid-state reaction, and their distinct phases were confirmed via rigorous X-ray diffraction (XRD) characterization. We then proceeded to create the composites by manually blending these complex oxides with epoxy, polyurethane, and silicone rubber matrices. The central focus of the study was to examine the impact of varying volume fractions of the complex oxide fillers on the dielectric properties of the composites in the frequency range of 4 – 8 GHz.Our observations revealed a direct correlation between the content of the complex oxide filler and the dielectric properties, including the dielectric constant and dielectric loss. Specifically, the addition of 10 % by volume fraction of (1-x) CaWO4-xNa2WO4 (x = 0, 0.4), Na0.5Bi0.5Mo0.5W0.5O4, or Bi2Mo0.5W0.5O6 fillers to the respective polymer matrices led to a significant enhancement in both the dielectric constant and the loss tangent. Promising results were particularly evident in three composite formulations: the 10 % 0.4Na2WO4-0.6CaWO4/silicone rubber composite demonstrated a dielectric constant (εr) of 2.02 ´ 102 and a loss tangent (tanδ) of -4.07 ´ 10-1 at 7.1 GHz; the 10 % Na0.5Bi0.5Mo0.5W0.5O4/epoxy composite exhibited a dielectric constant of 1.37 ´ 102 and a loss tangent of -6.43 ´ 10-1 at 7.22 GHz; and the 10 % Bi2W0.5Mo0.5O6/polyurethane composite displayed favorable properties with a dielectric constant (ϵr) of 8.37x101 and a loss tangent (tanδ) of -3.4 ´ 10-1 at 7.12 GHz.These results suggest the suitability of these composite materials for a wide range of microwave technology applications, including wireless communication, radar systems, and various microwave devices.

Improvement of Microwave Dielectric Properties of MgTiO3 Ceramics by Ti-Site Complex Substitution

Improvement of Microwave Dielectric Properties of MgTiO3 Ceramics by Ti-Site Complex Substitution

Impedance spectroscopy, B-site cation ordering and structure–property relations of (1 − x) La[Al0.9(Mg0.5Ti0.5)0.1]O3–x CaTiO3 ceramics for 5G dielectric waveguide filters

Dense (1 − x) La[Al0.9(Mg0.5Ti0.5)0.1]O3–x CaTiO3 ceramics were synthesized via solid-state reaction. The crystal structure and microwave dielectric properties of the ceramics were systematically investigated. Rietveld refinement revealed that when x ≤ 0.2, the ceramics had a rhombohedral structure with an R-3c space group. When x ≥ 0.5, the ceramics had an orthorhombic structure with a Pbnm space group. Selected area electron diffraction and Raman spectroscopy analyses proved that the microwave dielectric ceramics had a B-site order, which accounted for the great improvement in microwave dielectric properties. The content of oxygen vacancies was identified through X-ray photoelectron spectroscopy, and the change rule of Q × f was closely related to oxygen vacancy content. The perturbation of A-site cations had an important influence on dielectric constant. Specifically, with the increase in Ti4+ content, the perturbation effect of the A-site cations was enhanced and dielectric constant increased. When x = 0.65, the temperature coefficient of resonant frequency of the (1 − x) La[Al0.9(Mg0.5Ti0.5)0.1]O3–x CaTiO3 microwave dielectric ceramics was near zero. The optimal microwave dielectric properties of 0.35LaAl0.9(Mg0.5Ti0.5)0.1O3–0.65CaTiO3 were εr= 44.6, Q × f = 32,057 GHz, and τf= +2 ppm/°C.

Structural investigation and improvement of microwave dielectric properties in Ca1-xBaxTiO3, low loss ceramics

Structural investigation and improvement of microwave dielectric properties in Ca1-xBaxTiO3, low loss ceramics

Structural investigation and improvement of microwave dielectric properties in Ca(HfxTi1-x)O3 ceramics

Calcium hafnium titanate, Ca(HfxTi1-x)O3 (CHT) was prepared using the conventional solid state reaction route. The X-ray diffraction patterns were used for analyzing the phase compositions. The XRD patterns revealed the arrangement of a single phase perovskite structure and therefore the structure is transformed from non-centrosymmetric orthorhombic (Pbnm) to centrosymmetric cubic (Pm-3m) at 0.4 ≤ x. Lattice parameter, crystallite size, densities and porosity were calculated. The SEM morphology of CHT at various hafnium (x), which is comprises of round-rod shaped grains with small pores microstructure. The substitution of Hf4+ ions over Ti4+, the microwave dielectric constant (ε r) decreases from 145 to 52, while the quality factor (Qxf) increases from 8105 to 24305 GHz and temperature coefficient of resonant frequency tuned towards zero τ f ∼ 4.5 ppm °C−1. Good combination of microwave dielectric material properties was accomplished for the composition x = 0.8 (at 3 GHz).

Improvement of microwave dielectric properties of Ba2Ti9O20 ceramics using [Zn1/3Nb2/3]4+ substitution for Ti4+

Ba2[Zn1/3Nb2/3]xTi9−xO20 (x = 0–0.5) ceramics with high-quality factors were successfully prepared via traditional solid-state method. In this work, the microstructure and microwave dielectric properties of the samples were studied. The X-ray diffraction patterns indicated that two different phases BaTi4O9 and Ba2Ti9O20 existed at x = 0, while the phase of Ba2Ti9O20 was found gradually dominating in specimens with the doping of [Zn1/3Nb2/3]4+. At the level of x = 0.5, a fraction of the monoclinic phases of Ba2Ti9O20 were transformed into the triclinic phase. Furthermore, the SEM and relative density were used to confirm the homogeneous microstructure of the Ba2[Zn1/3Nb2/3]xTi9−xO20 ceramics. The doping of [Zn1/3Nb2/3]4+ can effectively improve the microwave properties of Ba2Ti9O20 ceramics, which are shown as the increase of dielectric constant, quality factor, and the stability of temperature coefficient. Particularly, the excellent microwave dielectric properties were achieved for the Ba2[Zn1/3Nb2/3]0.3Ti8.7O20 ceramics sintered at 1300 °C, with er ~ 39.3, a high Q × f ~ 43,879 at 6 GHz, and a τf ~ + 7 ppm/°C.

Effects of LBSCA glass addition on the sintering characteristic and microwave dielectric properties of ZnTiNb2O8 ceramics

In this study, ZnTiNb2O8-xLBSCA (x = 0, 0.2, 0.4, 0.6, 0.8, and 1 wt%) ceramics were synthesized via solid-phase reaction. Effects of different contents of LBSCA glass on the sintering characteristic, phase composition, microstructure, and microwave dielectric properties of ZnTiNb2O8-xLBSCA ceramics were investigated in detail via X-ray diffraction, scanning electron microscopy, and Rietveld refinement analysis. Rietveld refinement result confirmed the existence of main phase ZnTiNb2O8 and secondary phase ZnNb2O6 in all samples, and the content of secondary phase decreased with increasing x. LBSCA glass obviously promoted grain growth, densification, and ordered arrangement of grains, which was conducive to good microwave dielectric properties. In general, the addition of LBSCA glass contributed to a decrease in sintering temperature to 950 °C, as well as improvement in microwave dielectric properties of ZnTiNb2O8 ceramics. ZnTiNb2O8-0.4wt%.LBSCA ceramics sintered at 950 °C showed excellent optimal properties of $${\varepsilon }_{r}$$ = 33.826, $$Q\times f$$ = 49,143 GHz, and $${\tau }_{f}$$ = $$-57.59 {\rm ppm}/^\circ{\rm C }$$ . Therefore, this ceramic can act as potential candidate for low-temperature fired material and promisingly be applied to multilayer filters and antennas.

Improvement in microwave dielectric properties of Sr2TiO4 ceramics through post-annealing treatment

Sr2TiO4 ceramics were synthesized via the conventional solid-state reaction process, and the effects of post-annealing treatment in air on the microwave dielectric properties and defect behavior of title compound were investigated systematically. The Q × f values could be effectively improved from 107,000 GHz to 120,300 GHz for the specimens treated at 1450 °C for 16 h. The thermally stimulated depolarization currents (TSDC) revealed two kinds of defect dipoles [ $$ \left({\mathrm{Ti}}_{\mathrm{Ti}}^{\hbox{'}}-{V}_{\mathrm{O}}^{\bullet \bullet}\right) $$ and $$ \left({V}_{\mathrm{Sr}}^{"}-{V}_{\mathrm{O}}^{\bullet \bullet}\right) $$ ] and oxygen vacancies $$ \left({V}_{\mathrm{O}}^{\bullet \bullet}\right) $$ were considered the main defects in Sr2TiO4. Under a post-annealing treatment in air, the concentrations of such defects in the ceramics decreased. Meanwhile, the impedance spectrum revealed the activation energy of the grain boundaries increased. These evidences could account for the improvement of Q × f values. Accompanied with a high er of 40.4 and a large τf of 126 ppm/°C, the enhanced high-Q Sr2TiO4 ceramics can be good candidates for applications in wireless passive temperature sensing.

Microstructure, phase evolution and interfacial effects in a new Zn0.9Mg0.1TiO3-ZnNb2O6 ceramic system with greatly induced improvement in microwave dielectric properties

Zn0.9Mg0.1TiO3-ZnNb2O6 (ZMT-ZN) ceramics was synthesized and characterized successfully for the first time, and phase conversion to secondary phases was largely restrained due to the introduction of ZnO nano inhibitors. Excellent microwave dielectric properties and optimal combination were achieved for the ceramics sintered at 1100°C, i.e., εr=27.5, Q×f=75,000GHz, τf=−3.8ppm/°C. Particularly, the comparatively insulated interlayers were considered as the key mechanism to impede transportation or transfer of defects and surface polarization charges. Considering the merits of facile, low cost and simple process, this series of ZMT-ZN ceramics are promising new candidates for ultra-low microwave devices.

Solid-state reaction mechanism and microwave dielectric properties of 0.95MgTiO3–0.05CaTiO3 ceramics

In this work, a method (marked as MCT1) to simplify the production process of MgTiO3–CaTiO3 ceramics was investigated. For the MCT1, MgTiO3–CaTiO3 ceramics were prepared by using the MgO, CaCO3 and TiO2 powders without preparing MgTiO3 and CaTiO3. For the traditional method (marked as MCT2), the CaTiO3 and MgTiO3 powders were firstly synthesized and then mixed to prepare MgTiO3–CaTiO3 ceramics. The MCT1 inhibited the formation of MgTi2O5 phase and improved the sintering behavior of ceramics, which resulted in the improvement of microwave dielectric properties for MgTiO3–CaTiO3 ceramics. The good microwave dielectric properties of e r = 19.4, Q × f = 101,951 GHz, and τ f = −15 ppm/°C were obtained for MCT1 ceramics.

Improvement of microwave dielectric properties for Ba(Ni1/3Nb2/3)O3 ceramics by Zr-substitution

Effects of Zr-substitution on the structure, microstructure and microwave dielectric properties of Ba(Ni1/3Nb2/3)O3 ceramics have been investigated. A small amount of Zr-substitution facilitates the densification of Ba(Ni1/3Nb2/3)O3 ceramics. Within x≤0.05, the densification temperature decreases with increasing x in Ba[(Ni1/3Nb2/3)1−xZrx]O3, while it turns to increase for x>0.05. With increasing x, the grains become more homogeneous and closely contacted, and significantly increase in size for x=0.15–0.20. The B-site cations 1:2 ordering is destroyed by Zr-substitution, and only stabilizes for x≤0.04. B-site cations 1:1 ordering starts to form in x=0.04, and the 1:1 ordering degree first increases and then decreases with increasing x. Qf value decreases slightly in x=0.01 and then increases monotonously with x increasing from 0.02 to 0.20. The destroyed 1:2 ordering structure is responsible for the decreased Qf value in x=0.01, while the improved grain configuration dominates the increase of Qf value for x=0.02–0.20. The dielectric constant εr increases monotonously with increasing x, due to the higher polarizability of Zr ion than the average value of Ni/Nb ions. The temperature coefficient of resonant frequency τf shifts from negative to positive through zero with increasing x, which is ascribed to the highly positive τf value of the end member BaZrO3. The significant improvement of microwave dielectric properties has been achieved for x=0.10, higher εr, higher Qf as well as near zero τf value have been obtained: εr=31.8, Qf=36,100GHz, τf=7.8ppm/°C.

Improvement in microwave dielectric properties of La(Mg0.5Sn0.5)O3 ceramics by applying ZnO–B2O3–SiO2

The microwave dielectric properties of ZnO–B2O3–SiO2 (ZBS)-doped La(Mg0.5Sn0.5)O3 ceramics were investigated with a view to their application in microwave devices. ZBS-doped La(Mg0.5Sn0.5)O3 ceramics were prepared by the conventional solid-state method. The X-ray diffraction patterns of ZBS-doped La(Mg0.5Sn0.5)O3 ceramics exhibited no significant variation of phase with sintering temperature. By adding 2.0 wt% ZBS, a dielectric constant of 19.14, a quality factor (Q × f) of 35,800 GHz, and a temperature coefficient of resonant frequency τf (−86 ppm/°C) were obtained when La(Mg0.5Sn0.5)O3 ceramics were sintered at 1,400 °C for 4 h.

The Improvement of Microwave Dielectric Properties on Al2O3 Ceramics

Al 2 O 3 ceramics are a candidate for millimeter-wave dielectrics. It possesses a high quality factor (Q·f) and a low dielectric constant (ϵ r ), however, a relatively large negative temperature coefficient of resonant frequency (τ f ) is an obstacle. For microwave communicating application, a τ f value near 0 ppm/°C is desirable to keep the frequency stability at various temperatures. On the other hand τ f of TiO 2 is positive value, indicating that the τ f can be improved by doping TiO 2 in Al 2 O 3 . However 0.9Al 2 O 3 -0.1TiO 2 sintered above 1350°C were composed of three phases: Al 2 O 3 , TiO 2 and Al 2 TiO 5 . The τ f value was about -20 –30 ppm/°C. By annealing in 1000–1100 °C, τ f value approached to be 0 ppm/°C with decomposition of AlTi 2 O 5 . A good Q·f was obtained by optimizing the annealing condition.

Effect of Nonstoichiometry on the Structure and Microwave Dielectric Properties of Ba(Mg0.33Ta0.67)O3

The effect of a slight A- and B-site cation nonstoichiometry on the structure, densification, and microwave dielectric properties of Ba(Mg1/ 3Ta2/3)O3 (BMT) was investigated. Magnesium and barium nonstoichiometric compositions based on Ba(Mg0.33-xTa0.67)O3 [x = −0.015, −0.010, −0.005, 0.0, 0.005, 0.010, 0.015, 0.020, 0.025, and 0.030] and Ba1-x(Mg0.33Ta0.67)O3 [x = −0.015, −0.010, −0.005, 0.0, 0.0025, 0.005, 0.0075, 0.010, 0.015, 0.020, 0.025, and 0.030] were prepared using the conventional solid-state ceramic route. The lattice distortion and cation ordering were determined using X-ray diffraction technique. The phase composition and surface morphology were studied by EDX and scanning electron microscopy techniques, respectively. The sintered samples were characterized in the microwave frequency range using the resonance technique. It is found that a slight barium or magnesium deficiency can improve density, microwave dielectric properties, and cation ordering, while the addition of excess ions deteriorated them. The improvement in microwave dielectric properties was more pronounced in barium nonstoichiometric samples. Microwave dielectric properties of Ba0.9925(Mg0.33Ta0.67)O3 [εr = 24.7, τf = 1.2 ppm/°C, Quxf = 152 580 GHz] and Ba(Mg0.3183Ta0.67)O3 [εr = 25.1, τf = 3.3 ppm/°C and Quxf = 120 500 GHz] were found to be better than stoichiometric BMT [εr = 24.2, τf = 8 ppm/°C and Quxf = 100 500 GHz]. Raman spectroscopy was employed to study the effects of nonstoichiometry and related lattice distortions in BMT ceramics on their vibrational modes. Raman results clearly showed the 1:2 ordered structures of these materials with all active modes assigned. The spectra showed variations in the normal modes as a function of the composition. Also secondary phases contributed to the changes in the Raman spectra observed in compounds with x ≥ 0.02.